Refrigeration and liquefaction systems for the liquefaction of natural gas and other methane-rich gas streams are well known in the prior art. Cascade refrigeration systems using various multicomponent refrigerants have also been disclosed.
The prior art has also taught the combination of a cascade refrigeration system with a multicomponent refrigerant. For instance, in U.S. Pat. No. 3,763,658, a refrigeration and liquefaction system is set forth wherein a single component refrigerant and a multicomponent refrigerant are utilized in a cascade fashion to cool and liquefy a natural gas or methane-rich stream. It is disclosed to cool the multicomponent refrigerant with the single component refrigerant. In addition to the cooling of one refrigerant by the other refrigerant, the systems generally utilized ambient water found at the site of the liquefaction plant to aftercool the refrigerants during the compression of the same on the warm end of the refrigerant cycle.
Variations in the ambient temperature of such cooling water affects the demands on compressor drivers in the various refrigeration cycles and requires the selection of differing driver components depending upon those ambient conditions. This latter situation poses a problem for the matching of equipment parts and incurs a complexity and cost in the initial system and in the maintenance of replacement parts and the system as a whole.